1. Field of the Invention
The present invention relates to an apparatus for automatically adjusting a light axis or lighting area of a light beam emitted from a vehicle headlight in the horizontal direction on the basis of a steering angle.
2. Description of the Background Art
Such an apparatus of the type as mentioned above is disclosed, for example, in Japanese Patent Application Laid Open Nos. 2002-19517 and 2002-234383.
The former document discloses a technique for emitting a light beam in a specific light distribution pattern depending on a vehicle's running state from a headlight including a lamp body and a lighting unit disposed within the lamp body. More specifically, the light distribution pattern can be varied depending on not only a speed of an instant vehicle but a distance from another vehicle ahead of the instant vehicle. The latter document describes a technique for varying a width and a direction of a light beam emitted from a headlight depending on a vehicle speed, a vehicle height, etc. in order to perform headlight illumination best suited to a vehicle's running state.
Conventionally, a plurality of control maps whose parameters are a steering angle and a vehicle speed have been used to determine a controlled variable (an amount of control) for adjusting the direction of the light axis of the vehicle headlight on the basis of the steering angle and the vehicle speed. However, the prior art systems using such control maps have a problem in that, when a control map currently used is switched to another control map as a consequence of a change in the vehicle speed, the direction of the light axis of headlight may change abruptly because of the difference between the controlled variables which these two different control maps define, respectively. Such an abrupt change in the direction of the light axis of the headlight often causes the driver to feel awkwardness in the control of the light distribution pattern or light beam pattern.